Broach



H. D. CROFT July 17, 1928.

BROACH Filed Sept. 20, 1927 INVENTOR.

W M ;:.M Q 6% A TTORNE Y.

, shorter stroke (after the cutting element and Patented July 1,,7, 1928.

UNITED STATES PATENT'OFFICE.

HIRAM D. CROFT, 0F SPRINGFIELD, MASSACHUSETTS, ASSIGNOR TO PERKINS MACHINE AND GEAR COMPANY, OF SPRINGFIELD, MASSACHUSETTS, A CORBORATION OF MAS- SACHUSETTS.

BROACH.

Application filed- September 20,1927. Serial No. 220,656.

gear blanks, sprocket-wheel blanks, and the like, for the formation of teeth thereon, and resides in two or more roughing-cutting elements and a finishing-cutting element arranged in stepped relationship, said finishing-cutting element being located side by side with one and in line with another of said roughing-cutting elements, together with such other parts and members as may be necessary or desirable in order to render the broach complete and serviceable in every respect, all as hereinafter set forth.

The primary object of my invention is to produce means whereby it is possible to do a given amount of work (broaching) with a breaching elements, and consequently in less time, than has heretofore been possible, thus greatly expediting and facilitating the operation of cutting slots in blanks to convert them into gears or sprocket-wheels, and slots in other objects. 7

Other objects and advantages will appear in the course of the .-following description.

Although I have illustrated my invention as applied to a broach which comprises a set of three roughing-cutting elements, a pair of two different roughing-cutting elements,

and a finishing-cutting element, ,or five.

roughing-cutting elements, with the finishing-cutting element, inall, it is to be understood that roughing-cutting elements, with a finishingcutting element, or a number greater than five of the roughing-cutting elements, with a finishing-cutting element, provided they are arranged in stepped formation or relationship, with the finishing-cutting and a given number of roughing-cuttingelements placed side by side in one major group, and roughing-cutting elements placed side by side and forming minor groups with each succeeding minor group decreasing'by one, until at the end opposite to said major group there is a single roughing-cutting element. Always there must be a line comprising afinishingone or more roughingcutting elements, and a shorter line of one or more roughing-cutting elements, there being as many progressively shortenedlines, in addition to the -fi1'st,"as there are rough ing-cutting elements in the first.

first) of the there may be only two of the I attain the objects and secure the advan- 'tages of my mvention by the means illustrated in the accompanying drawings, in which Figure 1 is a front elevation of a broach which embodies a practical example of my invention Fig. 2, a transverse vertical section through said broach, taken on lines 2 2, looking in the direction of the assoclated arrow, in Fig. 1; Fig. 3, an enlarged, transverse section through the broach, on lines 3-3, looking down, in Fig. 1; Fig. 4, a detail associated with Fig. 3; Fig. 5, an enlarged, transverse section on lines 5-5, looking down, in Fig. 1, and, Fig. 6, an enlarged, transverse section on lines 66, looking down, inFig. 1.

In each of Figs. 3-, 5, and 6, a fragmentary portion of a gear blank, whichin fact (assumedly) is being cut with my broach, is

to a reciprocating member (not shown) forming part of a machine of any suitable type adapted to employ this broach. The holder 4 on the front side is provided with longitudinah'parallel flanges 7 and 8 spaced apart to receive between them the cutting elements hereinafter described. Abutment blocks 9, 10, and 11 are introduced between the flanges 7 and 8 in the order named commencing at the top, and are secured by bolts or'other means to said flanges.

There are in this broach six cutting elements 'or cutters, and they comprise a set of three cutters 12 all substantially alike S imilar reference characters 'designate vsimilar parts throughout the several views.

and arranged in stepped relationship, a set of two cutters 13 both substantially alike and also arranged in stepped relationship, and a cutter 14.

One each of the cutters 12 and 13 and the cutter 14 are received between the flanges 7 and 8 laterally, and between the uppermost abutment block ,9 and the intermediate abutment block 10 longitudinally; another of the cutters 12-and the other cutter 13 are receivedbetween said flan es below said intermediate abutment blo k; and the third cutter. 12 is-received between said flanges, and between the abutment block 11 and the last-named cutter 13. 'One of the cutters' 13 is directly below the cutter 14, and one of the cutters 12 is directly below said cutter" 13,. all being in line with each other and immediately adjacent to the inner face of the flange 8. Likewise the other cutter l3 and one of the other cutters 12 are in line with each other, on the inner sides of the cutter 14 and the cutter 13 below said firstnamed cutter, respectively. The remaining cutter 12 is located against the inner face of the flange 7. A spacer or separator 15 is inserted between the cutters 12 and 13 in the upper, major or main group of three, a separator 16 is inserted between said cutter 13 and the cutter 14, a separator 17 is inserted between the cutters 12 and 13 in the lower the set of three, and a. filler 21 is insertedbetween the adjacent sides of said flange and the lowermost cutter 12, said fillers at the ends being in abutting relationship with each other and with the blocks 10 and 11, respectively.

The cutters, spacers, and fillers, in the channel between the flanges 7 and 8, are securely held in place therein by means of a plurality of bolts 22 and nuts 23. As shown in Figs. 3, 5, and 6, each bolt 22 has at one end a head 24 that is received in a transverse passage in the flange 7 there also being in said passage between said head and the uppermost roughing cutter 12,- the filler 20, or the filler 21, as the case may be, a loose sleeve 25, through which said bolt passes. A lock pin 26 is inserted in adjacent grooves, in each head 24 and the wall of the passage in which said head is received, to prevent the head and its bolt from turning when one of the nuts 23 is screwed onor off of said bolt. Each bolt 22, at the end opposite to that-where its head 24' is located, projects beyond the right-hand side of the flange 8 to receive one of the nuts 23. i

The teeth of the cutter 14 are of the full size and form or shape of the slots finished thereby in the blank 1 to, form or complete the gear teeth on said blank, but the teeth of the cutters 13 are of a more rudimentary character, and the teeth of the cutters 12 are of a still more rudimentary character. Each of the cutters 12 is narrower than either of the cutters 13, and each of the latter is nar- [rower than the cutter 14. The cutter 14 is p a finishing cutter, whileeach of the other cutters is a roughing ened by the lower roughing cutter 13', and onecut is made with the intermediate roughing cutter 12, said cutters dofno more work on the gear being broached, because the remainder of the work is done by the uppermost roughing cutter 12, the upper roughing cutter 13, and the finishingcutter 14. Subsequent, therefore, to the first full-length stroke of the broach,- the length of the stroke of said broach is cut down or reduced to approximately one-third of that of 'said first stroke. It is seen, therefore, that, with this broach, the operation of gear cutting is very materially expedited over the operation wherein is employed a broach having only one long cutting memberfor the equivalent, with which to do the entire work. In this latter case it is necessary that the broach make a full-length stroke each and every time it is operated effectively, instead of merely about one-third of a full-length stroke after the first one, as with my broach.

Each roughing cutter 12 is adapted to broach only a guide slot, so to speak, for one of the roughing cutters 13 to enlarge, and the finishing cutter 14 to complete and convert into a true gear teeth slot.

When the broach descends the first time and makes its single full-length stroke, aslot action on the work of the lowest roughing cutter 12, the intermediate roughing cutter 12 broaches a slot in the work at the left of time the finishing cutter 14 is making its out,

the upper roughing cutter 13 passes through and enlarges and deepens the second slot cut in the gear blank, and the uppermost roughing cutter 12 broaches another slot therein at the left of said second slot, as illustrated in Fig. 3. Thus one complete slot and two rudimentary slots are cut in the blank 1. Next in order the broach is elevated to locate the uppermost roughing cutter 12, the upper roughing cutter 13, and the finishing cutter 14' above the blank, said Hulk is indexed, and said'broach is caused to descend again. At the second descent of the broach, the finishing cutter 14 converts the secondslot in the blank into a complete slot, the upper roughing cutter 13 enlarges and deepens the third slot in said blank, and the uppermost roughing cutter 12 broaches another-slot therein, The broach at this time makes astroke of about one third of the length of the first stroke made by it, and contimes-thereafter to have there to an up and down motion which in length corresponds with that of the second stroke. The three upper cutters continue to duplicate the cut-s just described until the last slot in the blank is finished by the cutter 14, the blank being indexed for each complete slot. The broach is moved downwardly to make its out and finally'its last cut, after being indexed each time, and thereafter upwardly to initial position. It is while the broach is at the upper end of its travel, either about to finish its ascent or about to commenceits descent, or during the change of direction of movement at such point, that the indexing operation occurs.

When the blank is placed in position to be cut, the broach must first make a. full-length stroke, as hereinbeforc explained, and then its stroke is shortened to correspond with the length of the group of three broaches, plus the necessary amount of overrun at each end. ()nly once, therefore, does the broach make its full-length stroke during the cutting of a gear.

The intermediate abutment block 10 separates the upper group of cutters from the group or pair below, so that the work when indexed can clear the cutters.

In any of my broaches the finishing cutter is always at the following end of the longest line of cutters, and the roughing cutters touching the outside oblique plane are all alike, those touching the next oblique plane areall alike, but different from those touching said outside plane, and so on. When there are only three cutters, the two roughing cutters are, of course, alike.

Each stroke after the first, of the cutter, is of a length which approximately corresponds with the length of said first stroke divided by the total number of lines of cutters, or of cutters in the main group, or in other words, is a little greater than the length of said group.

More or less change in the shape, size, construction, and arrangement of some or all of the parts of this broach may be made, without departing from the spirit of my invention, or exceeding the scope of what i is claimed.

What I claim as my invention, and desire to secure by Letters Patent, is-

1. A broach havin a plurality of series of finishing and roughing cutters arranged in ofi'set stepped relationship, at least one of said series having a finishing and a roughing cutter in longitudinal alignment, and at least one other of said series comprising a single roughing cutter laterally placed relative to said finishing cutter, each successive series decreasing in length, and spaces between cutters of the same series to allow for indexing the work,'whereby it is possible to reduce in length the strokes of the broach, after the first stroke thereof, for the performance of a given amount of work.

2. A broach having a plurality of outside and intermediate series of finishing and roughing cutters arranged to bffset stepped relationship, one outside series having finishing and roughing cutters in longitudinal alignment, the other outside series comprising a single roughing cutter laterally placed relative to the finishing cutter, and each intermediate series of roughing cutters in iongitudinal alignment, the cutting part of each rougl'iing cutter in each intermediate series differing from the cutting parts of the others in the same series, but being like the cutting parts of roughing cutters in other series, the roughing cutters which are alike being relatively ofiset, each series decreasing in length, and spaces between cutters of the same series to allow for indexing the work,.

whereby it is possible to reduce in length the strokes of the broach, after the first stroke thereof, for the performance of a given amount of work.

3. A broach having a plurality of series of finishing, intermediate and roughing cutters arranged in offset stepped relationship, one series having a finishing, an intermediate and a roughing cutter in longitudinal alignment, a second series with an intermediate cutter adjacent and laterally placed rela-' tive to the finishing cutter of the first series and having a roughing cutter in longitudinal alignment therewith, and a third series comprising a single roughing cutter adjacent and laterally placed relative to the intermediate cutter of the second series, each successive series decreasing in length and spaces between cutters of the same series to-allow for indexing the work, whereby it is possible to reduce in length the strokes of the broach, after the first stroke thereof, for the performance of a given amount of work.

. HIR-AM CROFT. 

